A boronic acid functionalized terbium metal-organic framework for fluorescence detection and adsorption of gallic acid.

Gallic acid (GA) is widely applied as an antioxidant in foods and pharmaceuticals. In this study, a boronic acid functionalized metal-organic framework (Tb-MOF) is developed for fluorescence detection and adsorption of GA. Tb-MOF is constructed by coordination polymerization of terbium ions (Tb³⁺) with 3,5-dicarboxyphenylboronic acid (BBDC). The resulted Tb-MOF exhibits green fluorescence emission at 546 nm under an excitation of 280 nm. However, the green emission of Tb-MOF decreases in the presence of GA due to the formation of borate esters between phenolic hydroxyl groups of GA and hydroxyl groups of Tb-MOF. Under optimized conditions (40 mmol·L^-1 Tris-HCl buffer solution of pH = 6.2 and reaction time of 25 min), the sensor shows a wide detection range of 5 ∼ 200 μmol·L^-1 with a correlation coefficient (R²) of 0.9950. Meanwhile, Tb-MOF shows good selectivity and sensitivity to GA (the limit of detection (LOD) is 0.44 μmol·L^-1). Additionally, Tb-MOF is used to investigate GA adsorption. The corresponding adsorption data can be suitably described by Langmuir isotherm and pseudo-second-order models with a maximum adsorption capacity of 6.03 mg·g^-1. The above results demonstrate the potential of prepared Tb-MOF in integrating GA detection and adsorption in water samples.